Process for making rough surfaced filaments



Nov. 30, 1954 w. A. HARE PROCESS FOR MAKING ROUGH SURF ACED FILAMENTS Filed Dec. 13, 1949 INVENTOR. Weston Andrew-Hare BY ATTORNEY ill fibers, yarns, monofilaments and the like having a rough surface and, in particular, 'tothe preparation of synthetic staple fibers which can be spun into yarns of high tensile strength and improved .processability.

"Synthetic filaments and yarns commonlyprepared by "extrusion through fine orifices by -th'e-' dry-, wetor meltspinning techniques, generally-possess a smooth surface. Although the'cross-section of such filaments maybe other than circular, for example dog-boned or cloverleaf in contour, fabrics made from such multifilament yarn possess a slick hand andare cold to "the touch. In addition, the smooth surface-of synthetic filaments 'makes for '"more difficult working of the synthetic staple fibers into spun yarn. 'The desired fiber cohesiveness is hot avail- "able. Thus, "the 'truestrength of synthetic fibers is not realized in -spun yarns made from smooth surface staple fibers. Natural fibers, such as wool and animal 'hair, have rough, seny surfaces, which tend. to interlock and contributeto the over-all'strengthgof the spun yarn. The scales also provide better heat insulation and lend a warm-to-the-touch quality to fabrics made from such yarn.

"It is an object of this invention to provide synthetic filaments and yarns having arou'g'h surface. Apar'ticul'ar object is to-p'rovide high -tensile strength filaments having rough surfaces. A' further object is toprepare rough surfaced filaments which can be cut into staple fibers and spun into high strength yarns of improved cohesiveness. 1(3ther objects will become obvious from the description elow.

The objects of this invention are accomplished by the process-of this invention which comprises spinning a melted plasticized lpolymer composition into filaments, the surfaces of which are considerablymore brittle than the cores, and drawingthe filaments about '50200% at a temperature at which'the yarn surface, but not the core, is brittle, and subsequently washing out the plasticize'xx. By, so doing, high tensile strength synthetic filaments having a 'roughsurface'can be prepared readily. The cold drawing operation causes the formation of a multitude of small cracks in the surface of the filament. These cracks extend only about one-s'ixth'of the radius of the. filament and do not destroy ,the inherent high tensile characteristics of the synthetic filaments. In fact, the filaments after washing out the plasticizer can be hot drawn to impart additional orientation and strength without destroying'the surface roughness. v p The process .of this. invention can best be understood byfrefe'rence to 'the followingv examples and figures. which are illustrative and not to-.be construed as limitative and in which parts and; percentages are by weight unless otherwise specified; In the figures:

Figure '1 shows a filament of .this invention having the desired rough surface and transverse cracks;

Figure 2 shoWs the normal, smooth-surfaced filament produced in control experiments; 1

Figure 3 is a cross-section of the filament of this invention of Figure 1 showing the rough surface and the transverse. cracks; and

Figure 4 is alcross-sect-ion of the normal smoothsurfaced yarn'of Figure 2.

Example I well mixed'composition coinp'risihg 52.5 parts "of ethylene cyclic carbonate and 47.5 parts of powdered Patented Nov. 30, 1954 polyacrylonitrile having a molecular weight of 40,000 (determined from the viscosity using the Staudinger equation) was placed in an autoclave at 130 C. from which it was forced to a metering pump. The metering pump maintained at 142 C. delivered the spinning melt at the rate of 8 grams/minute through a standard sand pack filter to ass'pinneret'having 10 holes, each'hole having a diameter of 0.012 inch. The filaments thus produced solidified rapidly in room temperature airand were collected on a perforated bobbin at the rate of 223 yds./min. with the aid of suitable guides. solidification was so complete that stuck filaments were 'not a problem. A sample of this ten-filament yarn was stretched at rooin temperature (2025 (3.) to twice'its original length and then washed in cold Water to remove the ethylene carbonate. There resulted a 'dull, soft yarn having the characteristics of the filament shown in Figure 1.

Example II Monofilaments were spun in the manner described in Example I from a melt comprising 50% polyacrylonitrile and 50% ethylene cyclic carbonate. Clear, light tancolored monofilainents were obtained at low speed. It was observed that cold drawing the plasticized monofilament at room temperature gave a highly broken surface with surface cracks extending about one-sixth of the radius of the fiber, while the interior of the fiber was undamaged. On the other hand, when theplasticized monofilament was hot drawn at 100 C. after washing out the plasticizer a clear, transparent filament with unbroken surface was produced.

Example III A spinning dope comprising 52 /2'% ethylene cyclic carbonate and 47%.% polyacryl'on'itrile was extruded through a 5-hole spinneret heated to 154 C. (hole diameter 0.007") in the manner described in Example I. The yarn thus formed was collected at the rate of 14 yds./ min. This yarn of heavy denier per filament was taken from the bobbin before washing and cold drawn (room temperature) twice. its original length between drums. The yarn was then washed and redrawn 4.2 times its length between rolls heated to temperatu res'of 123 C. A second sample of yarn was washed after spinning and then drawn 8.9 times its original length between rolls heated to temperatures of 125 C. ,The sample of yarn which was cold drawn prior to washing possessed a much less slick hand than the second sample, which had been washed and then hot drawn, and photomicrographs showed that the former had a rough, broken surface corresponding to Figure 1. A typical cross-section of this yarn is shown in Figure 3.

Example IV A 45/55 blend of polyacrylonitrile having a molecular weight of 70,000 in tetrarnethylene cyclic sulfone was prepared and spun into filaments in the manner described in Example I, the yarn obtained being collected at 100 yds./min. When the yarn prepared in this manner was drawn twice its original length at room temperature prior to washing, minute cracks appeared in the surface of the yarn. Subsequent washing to remove the tetramethylene sulfone gave a dull, soft, rough-surfaced yarn.

According to this invention, a yarn may be produced with a roughened surface with attendant increased surface drag, sewer) and fiber cohesiveness. This is a very desirable property in improving the workability of staple fiber and in increasing strength of spun staple yarns and fabrics prepared therefrom.

The procedure is to cold draw a plasticized fiber made up of polymer and plasticizer at a draw temperature and at a rate of draw, whereby on the outer surface of the fiber, the plasticity of the material is exceeded and considerable cracking and checking results. The inner portion of the fiber is not similarly affected under the conditions chosen because of a difference in brittleness of the inner and outer portions of the fiber. The outer portion of the filaments is more brittle because of loss of the solvent or plasticizer by volatilization from these surfaces during spinning. The nature 'of the surface cracks may be observed under a microscope. The surface of the cold drawn filaments is seen to have numerous cracks in many directions giving the appearance of crystals or facets covering the surface. Cross-section pictures show that the cracks extend only a short distance, up to about one-sixth of the radius, into the fibers. On hot drawing either the plasticized or washed yarns, the sharpness of the cracks is much reduced and the facets appear rounded but still are present.

Although the examples have described the application of this invention to the preparation of polyacrylonitrile filaments and yarns having a rough surface, the invention is not limited thereto. The essential cold drawing step which produces the surface cracks can be applied to undrawn filaments of any polymer mixed with a small amount of plasticizer or solvent, whereby the plasticizer has been partly removed from the outer portions of the filaments by volatilization or otherwise. Thus, any plasticized thermoplastic fiber-forming polymer can be used. The invention is particularly applicable to the preparation of rough surface filaments from such polymers as cellulose acetate, cellulose ethers, the high molecular weight polyamides, polyesters and polyesteramides, and the fiber-forming polymers and the copolymers of vinyl chloride, vinylidene chloride and acrylonitrile.

The plasticizer used should be a relatively high boiling material preferably water soluble, which is compatible with the polymer employed. The amount of plasticizer to be used depends upon the polymer and the spinning conditions to be employed. The essential requirement is that a yarn be prepared which is non-tacky at room temperatures and the outer surface of which is much more brittle than the core of the fiber. For the inherently lower melting polymers the amount of plasticizer required will be small, probably no more than 20%, based on the weight of the polymer. For polymers, such as polyacrylonitrile, which do not appear to melt, larger amounts of plasticizer, for example as much as 60% of the composition, may be required. The spinning conditions in turn must be adjusted for each polymer and plasticizer composition so that only a small amount of the plasticizer is removed from the yarn during the spinning process.

In view of the brittleness of the outer portion of the filaments and the brittleness to a less degree of the whole filament, the amount of cold draw which can take place is rather small, generally from 50200% depending upon the plasticized polymer yarn prepared. However, as shown in Example III, the yarn may be further strengthened and oriented without losing its rough exterior by completing the drawing at higher temperatures, such as 100 C. to 250 C., after washing in the usual manner. The definition of cold draw in this process must depend on the brittle temperature of the skin and core, respectively, and on the rate of draw. that for plasticized polyacrylonitrile melt spun filaments, room temperature and an ordinary rate of drawing suffices to differentiate between the outer and inner portions of the filaments and to produce a rough surface yarn.

For some plasticized polymer yarn colder temperatures and higher draw rates will be required to produce the desired effect. On the other hand, there are cases where drawing and temperatures somewhat above room temperature would still show the effect. In general, the cold drawing may be carried out at temperatures of C. to 40 C. While some stretching does occur in spinning this is done at elevated temperatures and is so small that very l1tt1e elongation and no orientation occurs, the spinning speeds being low.

The minute surface cracks, responsible for the roughsurface, obtainable by this process are not obtainable unless the plasticizer-laden yarn is cold drawn. Hot drawing before or after removing plasticizer with no c old drawing involved leads to smooth surface filaments like those 1n Figures 2 and 4. Cold drawing an unplasticized yarn does not give the desired result because of the brittleness of the yarn. According to the process of this invention, a plasticized filament having less plastic1zer in the skin than in the core is produced. The elasticlty of the skin is less than that of the core at temperatures of 40 C. or less and in the drawing at these relatively low temperatures, the elastic limit of the skin only is exceeded and the minute cracks appear in the skin only. Pecuharly, the cold drawing step must be done It so happens first; if the plasticized filament is first hot drawn and then cold drawn, rough surfaced filaments are not obtained. g

The process of this invention leads to the preparation of synthetic high tenacity filaments of increased surface roughness, drag or scroop. The filaments prepared in this manner have transverse cracks and scales on the surface. Fabrics prepared from these rough surface yarns, particularly staple yarns, have a warm wool-like hand. The rough surfaced filaments have improved processability as staple fibers due to the better fiber cohesion. Staple yarns of lower twist and better strength can therefore be prepared. Better fabric properties, such as reduced slip and better form stability, are inherent with the rough surfaced yarns prepared by the process of this invention.

Any departure from the above description which conforms to the present invention is intended to be included within the scope of the claims.

I claim:

1. A process for the production of rough surfaced filaments of acrylonitrile polymers which comprises melt spinning a plasticized acrylonitrile polymer; removing by volatilization some of the plasticizer so that the outer part has less plasticizer than the core; cold-drawing the resultant filaments at a temperature of 0 C. to 40 C.; removing the plasticizer and thereafter hot-drawing the iiezsultant cold-drawn filaments at a temperature of about 2. A process in accordance with claim 1 in which the said polymer is polyacrylonitrile.

3. A process in accordance with claim 1 in which the said plasticizer is ethylene cyclic carbonate.

4. A process in accordance with claim 1 in which the said plasticizer is tetramethylene cyclic sulfone.

5. A process for the production of rough surfaced filaments of synthetic polymers which comprises spinning a melted plasticized polymer; removing by volatilization a portion of the plasticizer in the resultant filaments so that the outer part has less plasticizer than the core; cold drawing the resultant plasticized filaments at a temperature of 0 C. to 40 C. to produce a roughened surface on said filaments; and thereafter removing the plasticizer from the resultant rough surfaced filaments.

6. A process in accordance with claim 5 in which the said cold drawing is done at a temperature of about C.

7. A process in accordance with claim 5 in which the said polymer is an acrylonitrile polymer.

8. A process in accordance with claim 5 in which the said polymer is polyacrylonitrile.

9. A process in accordance with claim 5 in which the said plasticizer is ethylene cyclic carbonate.

10. A proces in accordance with claim 5 in which the said plasticizer is tetramethylene cyclic sulfone.

11. A process for the production of rough surfaced filaments of synthetic polymers which comprises spinning a melted plasticized polymer;-removing by volatilization a portion of the plasticizer in the resultant spun filaments so that the outer part has less plasticizer than the core; cold drawing the resultant plasticized filaments at a temperature of from 0 C. to C. to produce a roughened surface on said filaments; thereafter removing the plasticizer; and then hot drawing the resultant cold-drawn rough surfaced filaments.

12. A process in accordance with claim 11 wherein the aesripeature used in the hot drawing is from C. to

13. A process for the production of rough surfaced filaments of acrylonitrile polymers which comprises spinning a melted plasticized acrylonitrile polymer; removing by volatilization a portion of the plasticizer in the resultant filaments so that the outer part has less plasticizer than the core; cold drawing the resultant plasticized filaments at a temperature of from 0 C. to 40 C. to produce a roughened surface on said filaments; removingthe plasticizer and thereafter hot drawing the resultant cold-drawn, rough surfaced filaments.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,354,744 Dreyfus Aug. 1, 1944 2,426,728 DAlelio 'Sept. 2, 1947 

5. A PROCESS FOR THE PRODUCTION OF ROUGH SURFACED FILAMENTS OF SYNTHETIC POLYMERS WHICH COMPRISES SPINNING A MELTED PLASTICIZED POLYMER; REMOVING BY VOLATILIZATION A PORTION OF THE PLASTICIZER IN THE RESULTANT FILAMENTS SO THAT THE OUTER PART HAS LESS PLASTICIZER THAN THE CORE; COLD DRAWING THE RESULTANT PLASTICIZED FILAMENTS AT A TEMPERATURE OF 0* C. TO 40* C. TO PRODUCE A ROUGHENED SURFACE ON SAID FILAMENTS; AND THEREAFTER REMOVING THE PLASTICIZER FROM THE RESULTANT ROUGH SURFACED FILAMENTS. 